NASA's Kepler telescope in trouble, future uncertain

The Kepler telescope's planet-hunting days could be over, with two of its reaction wheels stuck and potentially unable to keep the spacecraft's eye trained deep into space.

NASA engineers discovered Tuesday that the spacecraft had gone into safe mode, and when they tried to get one the wheels moving again, it was unresponsive.

They aren't giving up on Kepler yet, however. NASA will explore ways to get one of two nonfunctioning wheels moving again, and if they can't, Kepler might still be used for other exploration.

Meanwhile, there's still about two years of data that scientists can still sift through in efforts to discover more Earth-like exoplanets, outside our own solar system. Kepler already has helped identify 132 exoplanets and more than 2,000 unconfirmed candidates.

"We're not down and out, the spacecraft is safe, it's stable," Kepler deputy project manager Charles Sobeck said in a conference call with reporters. "The eventual performance we're going to get to, we just don't know at this time. "

There are four reaction wheels on the Kepler spacecraft, and three of them are needed to keep the telescope stable, surveying a small patch of sky for minuscule dips in starlight that might indicate the presence of an orbiting planet.

The technique is called the transit method, and Kepler's findings over the past four years have helped scientists determine that nearly every star in the universe has at least one exoplanet.

More discoveries are sure to be on the horizon, even if Kepler can't continue its mission.

"The most interesting, exciting discoveries are coming in the next two years," Kepler principal investigator William Borucki said.